docs: def string_to_data_time(d):
      '''
      simple parse date string, such as:
      2016-5-27 21:22:20
      2016-05-27 21:22:2
      2016/05/27 21:22:2
  
      2016-05-27
      2016/5/27
  
      21:22:2
      '''
      if d:
          d = d.replace('/', '-')
          if ' ' in d:
              _datetime = d.split(' ')
              if len(_datetime) == 2:
                  _d = _string_to_date(_datetime[0])
                  _t = _string_to_time(_datetime[1])
                  return _combine_date_time(_d, _t)
          else:
              # no space
              if '-' in d:
                  return date_to_datetime(_string_to_date(d))
              elif ':' in d:
                  return time_to_datetime(_string_to_time(d))
      return None